A typical asynchronous transfer mode (ATM) system provides for virtual path connections addressed by a 12-bit virtual path identifier (VPI) and virtual channel connections addressed by the VPI together with a 16-bit virtual channel identifier (VCI). Typically, virtual paths are large collections of various individual virtual channels. For example, one virtual path may contain hundreds of virtual channels. In many communication systems which involve ATM, the 12-bit VPI and 16-bit VCI are too large and cumbersome since there is no need for 4096 virtual paths and 65,536 virtual channels per virtual path. If memory and switching/control information is statically assigned for all possible connections 268,435,456 (4096.times.65,536) a large amount of memory is needed and wasted. In many cases only tens or hundreds of paths and connections are required.
At each ATM switch used for communication of data, a table of switching and control information must be maintained. Typically, in practice, the number of active connections on a typical 155.52 Mb/sec physical link is not expected to exceed 4,000 connections. Thus, the active portion of the switching information table is not required to be very large. However, in order to exploit the limited size of the number of active connections, a method to compress the 256 Meg possible virtual connections into a much lesser number active connections in a switching information table.
Clearly, using the full 28-bit VPI and VCI as an index to the switching information table is impractical for most applications and extremely inefficient and expensive. Using 256 Meg of memory for 4K active connections is a large waste of resources. Even indirect mapping for 256 Meg entries is impractical.